1. Field of the Invention
This invention relates generally to computer systems, and more particularly provides a system and methods for managing replication data, such as volumes.
2. Background
The proliferation of computing continues to increase the amount of data generated, transferred and stored, as well as reliance on the integrity of such data. Approaches to assuring data integrity generally fall into two categories: error handling and data backup.
Error handling can include determining whether data processed, transferred or stored appears to include errors, or further attempting to cause reporting or correction of determined errors. Examples of error handling mechanisms include but are not limited to data portion verification, version comparison, checksum calculation or re-transmission, among others.
Conventional data backup essentially provides for copying data stored in a “primary” storage to a typically separate “backup” storage copy such that: (1) after the backup copy is created, the copy can be restored to the primary storage data if a primary storage error is later detected, and (2) after the restoring, the restored primary storage data can again be reliably used. The particular storage device or media used for storing the backup copy can vary, and can reside locally, typically via a fixed interconnection to a tape or other removable media, or remotely, typically via a wired or wireless network to a remote backup system.
Typically, only an initial backup is completely conducted of all designated primary data. Thereafter, only primary data that has been modified since the last backup is stored to the backup copy. Most often, the primary storage maintains a primary storage change table indicating modified primary storage data portions. During backup, the change table is read sequentially, and where a table entry indicates a modified primary data portion, a copy of the modified data portion is transferred to the backup system. The backup system then either separately stores the copy of the modified primary data portion (e.g., as with versioning) or replaces the corresponding backup data portion with the modified primary data portion.
It is observed, however, that conventional backup systems can be problematic. For example, conventional backup systems fail to account for system errors that might occur during, rather than after, the backup procedure. The primary storage, transmission medium or backup storage might, for example, become inoperable after initiating and before completing storage of the backup copy. In such cases, the primary data, backup copy or both might be rendered unreliable should system operation be restored. Data backup might also be conducted with regard to a large amount of data, thereby rendering the applicable data largely inaccessible during backup, among other problems.
Accordingly, there is a need for methods and apparatus that enable data backup to be conducted, and also enable data loss due to system errors during a backup to be avoided. There is further a need for methods and apparatus that enable the backed up data to be more accessible and usable.